Self-position identification apparatus and self-position identification method

ABSTRACT

A position identification apparatus includes a storage section storing a position-unique information database containing, each position on a field and unique information generated from the signal strength of the reflected wave at the position in association with each other, an ultrasonic transmission section originating an ultrasonic wave assigned identification information, an ultrasonic reception section receiving the reflected wave of the ultrasonic wave, a unique information generation section generating signal unique information from the reflected wave, and a position identification section making a comparison between the signal unique information generated by the unique information generation section and the unique information included in the position-unique information database and identifying the current position.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority formthe prior Japanese Patent Application No. 2004-179822, filed on Jun. 17,2004; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invetion

This invention relates to a self-position identification apparatus and aself-position identification method of identifying the self-position bya single unit.

2. Description of the Relted Art

Hitherto, an autonomous mobile unit for freely moving in a field, suchas an automobile or a robot, has had a displacement amount detectionsensor such as a gyro or a pulse encoder as a method of detecting themove distance or the move direction for detecting the travel direction,the travel distance, etc. However, in detection of the displacementamount detection sensor, it is difficult to establish a complete methodof identifying the self-position singly by the autonomous mobile unitbecause of a slip on the move face, the accumulated error of the sensoritself, etc. Thus, various arts are designed for determining theself-position.

For example, an art of providing a signal originator aside from a mobileunit like the GPG (Global Positioning System) is generally known. (Forexample, refer to Japanese Patent Application (Kokai) No. 6-35535.) Inthe art disclosed in the JP-A-6-035535, a signal transmitter ispreviously installed indoors for transmitting and receiving a signal toand from a mobile robot, and the self-position is detected from the timerequired for transmitting and receiving the signal.

An art of providing intentionally a clue to determining theself-position is available. A mark such as a landmark is installed on amove route and the positional relationship with the installed mark isfound for identifying the self-position. (Refer to Japanese PatentApplication (Kokai) No. 2001-179668.)

An art of measuring the surrounding landform using a distance sensor andcomparing the landform with previously stored map information fordetermining a current position is also available. CAD data made up ofindoor shape data and attribute data indicating a reflectioncoefficient, etc., is held, an optimum sensor for conducting measurementis selected based on the attribute data, measurement is conducted usingthe selected sensor, and a comparison is made between the measurementvalue and the CAD data for identifying the self-position. Further, for alocation that cannot be detected with the sensor, a gyro, etc., is usedin combination to identify the position. (For example, refer to JapanesePatent Application (Kokai) No. 7-281753.)

However, the related arts involve the following problems: In the artdisclosed in the JP-A-6-35535, equipment needs to be previouslyinstalled and the preparation is intricate and in addition, the artlacks practicality depending on the application to use in an environmentwherein equipment cannot be installed for some reason, etc., and aproblem of poor feasibility results.

In the art disclosed in the JP-A-2001-179668, equipment is automaticallyinstalled and thus preparation is not required; however, for example,for use at home, if a mark is installed without permission, a problem oflimiting the life occurs. Identifying the self-position singly by anapparatus is preferred.

Further, in the JP-A-7-281753, an optimum sensor is selected based onthe attribute data. However, accurate landform data may be unable to beobtained with any sensor depending on the position by the effects ofabsorption, dispersion, transmission, etc., because of the complicatedenvironment, and it becomes difficult to accurately identify theposition in the complicated environment.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a self-positionidentification apparatus and a self-position identification methodcapable of accurately identifying the position regardless of whether theenvironment is simple or complicated and identifying the positionsingly.

According to one aspect of the invention, there is provided aself-position identification apparatus including storage device forstoring position association unique information provided by associatingposition coordinates and unique information indicating a unique featureamount associated with the position coordinates; transmission device fororiginating a detection signal assigned identification information; areception device for receiving a reflection signal corresponding to thedetection signal transmitted by the transmission device; generationdevice for generating signal unique information from the reflectionsignal received by the reception device; and identification device formaking a comparison between the signal unique information generated bythe generation device and the unique information associated with theposition coordinates included in the position association uniqueinformation and identifying the current position.

By thus configuration, it is possible to accurately identify theposition even in a complicated environment wherein a reflection signalaffected by disturbance of transmission, dispersion, absorption, etc.,or a wall, a floor, etc., forming a movable field or a secondary ortertiary reflection signal is received, for example.

Since complete position identification can be accomplished singly by theapparatus, it is possible to accurately identify the position even in anenvironment wherein a mark, an external auxiliary signal, etc., cannotbe installed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram to show the functional block configuration of amobile robot of a position identification apparatus according to theembodiment of the invention;

FIG. 2 is a drawing to show a state in which the mobile robot of theembodiment of the position identification apparatus transmits ultrasonicwaves radially from a move plane for coming in contact with a move face;

FIG. 3 is a drawing to show ultrasonic sensors annularly arranged totransmit and receive ultrasonic waves non-directionally with respect tothe move plane as the embodiment of the position identificationapparatus;

FIG. 4 is a drawing to show an ultrasonic sensor installed so as to scanevery given angle with the axis rotated to transmit and receiveultrasonic waves in every direction with respect to the move plane asthe embodiment of the position identification apparatus;

FIG. 5 is a drawing to show an example wherein the mobile robot of theposition identification apparatus according to the embodiment has theultrasonic sensors installed on the head;

FIG. 6 is a drawing to show an example wherein the mobile robot of theposition identification apparatus according to the embodiment has theultrasonic sensors installed on the periphery of the mobile robot;

FIG. 7A is a perspective view showing the ultrasonic waves aretransmitted from the ultrasonic sensors of the mobile robot;

FIG. 7B, 7C is a drawing showing examples of the mobile robot of theposition identification apparatus according to the embodiment of theinvention has ultrasonic sensors described in FIG. 7A;

FIG. 8 is a drawing to show an example of an ultrasonic signalcontaining code information for mobile unit identification transmittedfrom the ultrasonic sensor as the embodiment of the positionidentification apparatus;

FIG. 9 is a conceptual drawing to show a state in which the total signalunique information is found from signal unique information acquired ineach of the sensors placed annularly as the embodiment of the positionidentification apparatus;

FIG. 10 is a drawing to show filtering for changing the weight inresponse to the time for the reflected wave received from an ultrasonicreception section as the embodiment of the position identificationapparatus;

FIG. 11 is a conceptual drawing to represent lattice points indictingthe collection positions of unique information on a room drawing andunique information associated with the lattice points in aposition-unique information database as the embodiment of the positionidentification apparatus;

FIG. 12 is a drawing to show the structure of the position-uniqueinformation database as the embodiment of the position identificationapparatus;

FIG. 13 is a drawing to show paths to collect unique information fromthe position indicating a lattice point on a room drawing when themobile robot sets the move start position as the reference position asthe embodiment of the position identification apparatus;

FIG. 14 is a flowchart to show a procedure of usual processing of themobile robot of the embodiment of the position identification apparatus;

FIG. 15 is a flowchart to show a processing procedure of identifying thecurrent position of the mobile robot of the embodiment of the positionidentification apparatus;

FIG. 16 is a conceptual drawing to show lattice points indicatingpositions on a room drawing and calculated correlation values with themobile robot of the embodiment of the position identification apparatus;

FIG. 17 is a drawing to show a mountain-like distribution of thecorrelation values at positions in the whole field plane indicating aroom in the embodiment of the position identification apparatus;

FIG. 18 is a flowchart to show a processing procedure of identifying thedirection of the mobile robot of the embodiment of the positionidentification apparatus;

FIG. 19 is a flowchart to show a processing procedure untilidentification of the current position if the mobile robot of theembodiment of the position identification apparatus fails to identifythe current position; and

FIG. 20 is a drawing to show an example wherein a reflecting plate isinstalled ahead of an ultrasonic sensor to transmit and receive anultrasonic wave in all directions relative to the move plane as theembodiment of the position identification apparatus.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of a self-position identification apparatus or aself-position identification method according to the invention will bediscussed in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram to show the configuration of a mobile robot100 according to an embodiment of the invention.

As shown in FIG. 1, the mobile robot 100 of the embodiment is made up ofan ultrasonic sensor 101, a filtering section 104, a unique informationgeneration section 105, a position identification section 106, a maincontrol section 107, a move distance detection section 108, a movesection 109, a storage section 110, a camera 111, a feature amountextraction section 112, a reference position determination section 113,and a different robot signal removal section 114.

The ultrasonic sensor 101 is made up of an ultrasonic transmissionsection 102 and an ultrasonic reception section 103. In the embodiment,one device acts as the ultrasonic transmission section 102 and theultrasonic reception section 103, but the invention is not limited tothe mode. A dedicated device may be provided for each of the ultrasonictransmission section 102 and the ultrasonic reception section 103. Theultrasonic transmission section 102 forms a transmission device in theembodiment of the invention, and generates an ultrasonic wave accordingto input from the main control section 107 described later. Theultrasonic reception section 103 forms a reception device in theembodiment of the invention. The ultrasonic reception section 103receives a reflected wave resulting from reflecting the ultrasonic wavetransmitted from the ultrasonic transmission section 102 by a wall,etc., and outputs signal information of the received reflected wave tothe different robot signal removal section 114 described later.

FIG. 2 is a drawing to show a state in which the mobile robot 100 of theembodiment transmits ultrasonic waves radially from a move plane 202 forcoming in contact with a move face 201. As shown in the figure, themobile robot 100 uses the plane coming in contact with the move face 201at the current position of the mobile robot 100 as the robot move plane202, and transmits ultrasonic waves 203 radially from the move plane 202from the ultrasonic sensor 101.

In the embodiment, the ultrasonic sensor 101 is used as the transmissiondevice and the reception device, but the devices are not limited to thesensor in the embodiment of the invention. For example, an opticalsensor may be used. As the ultrasonic sensor 101 is used as thetransmission device and the reception device, the embodiment ischaracterized by the fact that the effects of the position and thestrength of the light source and the time of day and night as with theoptical sensor are not received when the self-position is identified.

FIG. 3 shows a placement example of the ultrasonic sensors 101 in theembodiment. In the example shown in FIG. 3, the directional ultrasonicsensors 101 are arranged annularly for artificially providingnon-directivity. After ultrasonic waves are transmitted at the same timefrom the ultrasonic sensors 101 arranged annularly, processing describedlater is performed, whereby it is made possible to identify the positionat high speed. In the embodiment, to simplify the description, it isassumed that the mobile robot 100 is provided with eight ultrasonicsensors 101 for originating ultrasonic waves at the same time, but thenumber of the ultrasonic sensors arranged annularly is not limited inthe embodiment of the invention.

As a different example from the embodiment, a placement example of anultrasonic sensor 401 is shown in FIG. 4. The directional ultrasonicsensor 401 can be rotated with the normal to the plane where a mobilerobot 400 moves as an axis. The ultrasonic sensor 401 rotates andtransmits an ultrasonic wave at every arbitrary angle and the reflectedwave of the ultrasonic wave is acquired. This operation is repeateduntil the ultrasonic sensor 401 makes a round, thereby performing a scanfunction equivalent to that of annular arrangement of the ultrasonicsensors 401. To rotate the ultrasonic sensor 401 for scanning, thenumber of the used ultrasonic sensors 401 is not limited. Specifically,when n ultrasonic sensors 401 are arranged at equal intervals on thesame circle, they may be rotated at least at 360/n degrees. Accordingly,there can be provided the mobile robot 100 having a scan functionequivalent to that of annular arrangement of the ultrasonic sensors andbeing more inexpensive regardless of the number of the ultrasonicsensors 401. The axis is not limited to the normal to the plane wherethe mobile robot 100 moves.

FIG. 5 is a drawing to show the mobile robot 100 with an unit composedof the ultrasonic sensors 101 installed on the head. As shown in thefigure, the mobile robot 100 has the ultrasonic sensors 101 installed onthe head and can move with wheels 301. The visual field is opened omnidirectionally, the mobile robot 100 does not become an obstacle toultrasonic waves, and it is made possible to reduce noise from anobstacle temporarily placed on a floor.

As a different example from the embodiment, FIG. 6 shows an examplewherein ultrasonic sensors 601 are installed on the periphery of amobile robot 600. The installation positions of the ultrasonic sensorson the mobile robot are not limited to those shown in FIG. 5 or 6 andthe ultrasonic sensors may be placed at any positions if ultrasonicwaves can be transmitted radially to the robot move plane 202.

For example, it is not limited that the ultrasonic waves are transmittedfrom the ultrasonic sensors 601 only in a direction parallel to therobot move plane. As shown in FIG. 7A, the transmitted ultrasonic wavesmay be substantially formed in spherical wave such as a dome-shape, or apart of the spherical wave to be rotation symmetry with respect to acenter axis perpendicular to the robot move plane 202. As shown in FIGS.7B and 7C, the ultrasonic sensor is annularly arranged around the centeraxis at predetermined angle from a direction of the robot move plane202. The annual arrangement of the ultrasonic sensors 601 may be notonly in one line but also in plural lines on the same axis line.Further, the predetermined angle at which the ultrasonic wave istransmitted from the ultrasonic sensors 601 can be changed in each lineof the annual arrangement when the annual arrangement of the ultrasonicsensors 601 is in plural lines on the same axis line.

In the embodiment, identification information is assigned to eachultrasonic wave transmitted from the ultrasonic transmission section102. FIG. 8 shows the ultrasonic wave transmitted with theidentification information assigned thereto. That is, usually as theultrasonic wave, five to ten pulses are transmitted all at a time at agiven frequency and as the vibration of the ultrasonic transmissionsection 102 is controlled so that the ultrasonic wave originationintervals differ, it is made possible to contain code information asidentification information unique to the mobile robot 100 in thetransmitted ultrasonic wave pulse group. The code information is used asidentification code.

Referring again to FIG. 1, the different robot signal removal section114 forms a removal device in the invention and removes the ultrasonicwave transmitted from any other mobile robot 100 based on theidentification code of the ultrasonic wave input from the ultrasonicreception section 103 of the ultrasonic sensor 101. If a plurality ofmobile robots 100 move in the same room and the ultrasonic wavestransmitted from the mobile robots 100 are mixed, the different robotsignal removal section 114 makes it possible to identify the accuratecurrent position.

The unique information generation section 105 forms a generation devicein the embodiment of the invention; it generates signal uniqueinformation indicating unique information at each position in a movefield from signal information of a reflected wave output through thefiltering section 104 described later, and outputs the generated signalunique information to the position identification section 106. In theembodiment, the signal strength of a reflected wave changing with theelapsed time since the reference time, the ultrasonic wave originatingtime, is used as the signal unique information. The signal strengthforms feature amount in the embodiment of the invention. The signalunique information for each sensor is totalized to generate the signalunique information of the robot position. FIG. 9 is a conceptual drawingfor totalizing the signal unique information acquired in each sensor tofind the total signal unique information of all sensors. Numerals 1 to 8shown in the figure indicate the ultrasonic sensors 101 installed on themobile robot 100, (1) to (8) indicate each the signal strength of thereflected wave changing with the elapsed time since the reference timein each sensor, and (9) indicates the sum total of the signal strengthof the reflected wave changing with the elapsed time since the referencetime in each sensor. As shown in the figure, the sensors are installedradially, so that the signal unique information of each sensor istotalized, whereby it is made possible to assume that it is the signalunique information proper to the position based on the reflected wavereceived from the radiation direction. Since the signal strength of thereflected wave changing with the elapsed time since the reference timeis used as the signal unique information, special operation to find thesignal unique information is not required and it is made possible toacquire the signal unique information at high speed. The signal uniqueinformation is not limited to the signal strength of the reflected wavechanging with the elapsed time since the reference time. For example,the frequency component calculated by conducting frequency analysis ofthe received reflected wave may be used as the signal uniqueinformation.

The filtering section 104 forms filtering device in the invention; itremoves noise by filtering from the signal information of the reflectedwave input from the different robot signal removal section 114 and thenoutputs the reflected wave signal information subjected to the filteringto the unique information generation section 105. Accordingly, it ismade possible to identify the current position if the reflected wavecontains noise.

FIG. 10 is a drawing to show the concept of the filtering performed bythe filtering section 104. In the figure, filtering is performed for thereflected wave signal information provided from the ultrasonic receptionsection 103, shown in graph (A) through filters F1 and F2 and thereflected wave signal information subjected to the filtering is shown ingraphs (B), (C), and (D). The filter F1 is a filter for reducing noiseproduced in the presence of an obstacle moving in the proximity of themobile robot 100 largely affecting the correlation (for example, a humanbeing or an animal). In contrast, filter F2 is a filter for reducingdistant, nonstationary disturbance noise. The graph (B) shows thereflected wave signal information output after being subjected to thefiltering through F1; the graph (C) shows the reflected wave signalinformation output after being subjected to the filtering through F2;and graph (D) shows the reflected wave signal information output afterbeing subjected to the filtering through F1 and F2.

The function of the filter F1 for reducing noise produced in thepresence of a nearby obstacle is a change function of the strength ofthe reflected wave signal information output in response to the timeuntil arrival of the reflected wave and more particularly is a functionof lightening the weight of the signal strength based on the arrivaltime of the reflected wave from the proximity. In the embodiment, theminimum signal strength is set to 0 V, but the invention is not limitedto it.

Time t1 in the graph indicating the filter F1 in FIG. 10 is referred toas first obstacle determination time. The first obstacle determinationtime forms first reference time in the embodiment of the invention andrefers to the ultrasonic arrival time used as the reference fordetermining that a reflected wave by an obstacle moving, etc., in theproximity of the mobile robot 100 (containing the case where a humanbeing, etc., temporarily passes through) after the mobile robot 100transmits an ultrasonic wave. If a reflected wave is received in thefirst obstacle determination time since the ultrasonic wave wastransmitted, the strength of the reflected wave signal informationoutput after through the filter F1 becomes the intermediate valuebetween the minimum signal strength and the signal strength of the inputreflected wave signal information. The specific value of the firstobstacle determination time changes depending on how much an object isclose to the mobile robot 100 to handle as an obstacle. In theembodiment of the invention, if an object existing within 0.5 m isdefined as an obstacle, 0.00292 sec found from the ultrasonic wavevelocity 343 m/sec becomes the first obstacle determination time. Thefirst reference time is not limited to the embodiment of the invention.The first reference time may be a time used as the reference fordetermining that the received signal is a signal reflected by anobstacle in the proximity of the reception.

The function of the filter F2 for reducing distant, nonstationarydisturbance noise is a change function of the strength of the reflectedwave signal information output in response to the time until arrival ofthe reflected wave and more particularly is a function of lightening theweight of the signal strength based on the arrival time of the reflectedwave from a distant location.

Time t2 in the graph indicating the filter F2 in FIG. 10 is referred toas second obstacle determination time. The second obstacle determinationtime forms second reference time in the embodiment of the invention. Thesecond obstacle determination time refers to the ultrasonic arrival timeused as the reference for determining that the received reflected waveis a reflected wave of distant, nonstationary disturbance noise afterthe mobile robot 100 transmits an ultrasonic wave. If a reflected waveis received after the expiration of the second obstacle determinationtime since the ultrasonic wave was transmitted, the strength of thereflected wave signal information output after through the filter F2becomes the intermediate value between the minimum signal strength andthe strength of the input reflected wave signal information. Thespecific value of the second obstacle determination time changesdepending on how much a received reflected wave is distant from themobile robot 100 to handle as disturbance noise considering the size ofa room and the maximum operation range of ultrasonic wave. In theembodiment, if the reflected wave at a distance of 5 m or more from themobile robot 100 is defined as disturbance noise, 0.0583 sec found fromthe ultrasonic wave velocity 343 m/sec becomes the second obstacledetermination time. The second reference time in the invention is notlimited to the embodiment, and may be a time used as the reference fordetermining that the received signal is a signal caused by distantdisturbance noise.

In the embodiment, filtering is performed by the filtering section 104after reception in the ultrasonic reception section 103, but theinvention is not limited to performing the filtering just afteracquisition of the reflected wave signal information. For example, it isalso possible to conduct frequency analysis on the reflected wave signalinformation by the unique information generation section 105 and thenfilter the frequency component after the frequency analysis using ahgihpass filter or a low-pass filter.

Referring again to FIG. 1, the position identification section 106 formsa position identification device in embodiment of the invention. theposition identification section 106 identifies the current position ofthe mobile robot 100 based on the signal unique information input fromthe unique information generation section 105 and unique informationregistered in a position-unique information database stored in thestorage section 110 described later. A processing procedure untilidentification of the current position of the mobile robot 100 and aprocessing procedure until determination of the initial direction at thecurrent position of the mobile robot 100 are described later.

The storage section 110 forms storage device in embodiment of theinvention. The storage section 110 stores a room drawing, theabove-mentioned position-unique information database, the currentposition, and position feature information. The storage section 110refers to a record medium of an HDD (hard disk drive), etc., forexample. The information stored in the storage section 110 is notlimited to them.

The room drawing stored in the storage section 110 refers to a drawingto show a room in which the mobile robot 100 moves. In the embodiment,the CAD data and the design drawing of the room are input, but the roomdrawing acquisition method is not limited to input of the CAD data orthe design drawing. For example, if the mobile robot 100 is firstinstalled in a room, the room may be measured using an included sensor,etc., and map information may be prepared.

The position-unique information database stored in the storage section110 forms position signal correspondence information in the embodimentof the invention. The position-unique information database retains theposition coordinates of each lattice point on the room drawing andsignal unique information collected at the lattice point in associationwith each other as unique information. The position-unique informationdatabase is used for the mobile robot 100 to identify the self-position.FIG. 11 shows the correspondence between each lattice point on the roomdrawing and the unique information. In the figure, the uniqueinformation is shown only for coordinates (b, 3) and coordinates (c, 3),but the position-unique information database retains all lattice pointsand the unique information in association with each other.

FIG. 12 shows an example of the data structure in the position-uniqueinformation database. In the figure, X and Y coordinates indicating thepositions of lattice points, the reflected wave signal strength in eachsensor and the total reflected wave signal strength in all sensors,received in the time resulting from separating the arrival time from thereference time at proper sampling interval, and the initial directionsof the mobile robot 100 on the room drawing at the unique informationcollection time are retained in association with each other. The initialdirections on the room drawing are represented by numbers of 1 to 8 sothat the numbers 1 to 8 correspond to the clockwise directions every 45degrees in such a manner that 1 indicates the north and 2 indicates thenortheast. The directions are used to identify the direction of themobile robot 100 at the moving time. What time period from the referencetime is held as the database is determined considering the ultrasonicwave velocity, the size of the room, etc. By the way, in the embodiment,eight sensors are included and the angle between the sensors becomes 45degrees. This means that the signal unique information collected foreach sensor is adopted as the unique information for each sensor. Theunique information for each sensor forms unique information for eachpiece of angle information in the invention. A plurality of pieces ofunique information can also be retained for one position in theposition-unique information database. The initial directions on the roomdrawing are not limited to the numbers of 1 to 8 and can be changedcorresponding to the number of the sensors installed on the mobile robot100.

In the embodiment, the unique information of all sensors and the uniqueinformation for each sensor are retained, but the invention is notlimited to the mode. For example, only the unique information of allsensors or only the unique information for each sensor may be retained.In addition, if the direction of the mobile robot 100 need not beidentified because the mobile robot 100 includes an azimuth detectionsection, etc., it is not necessary to retain the initial direction ofthe mobile robot 100 at the unique information collecting time.

The current position stored in the storage section 110 refers toinformation of the current position of the mobile robot 100 shown on theroom drawing in the movable range.

The position feature information stored in the storage section 110refers to storage information of the feature amount extracted from imagedata photographed by the camera 111 by the feature amount extractionsection 112 in association with the photograph position coordinates. Theposition indicated by the position coordinates retained in the positionfeature information is used as the reference position, and the featureamount extracted from the image data photographed at the referenceposition is used as the reference feature amount. The reference positionand the reference feature amount corresponding to the reference positionare used as the reference for first collecting unique information or isused when the current position is recognized if identifying the currentposition fails. The position feature information is used for determiningwhether or not the position is the reference position in the referenceposition determination section 113 described later. The number of thereference feature amounts stored as the position feature information maybe smaller than the number of pieces of the unique information.

The main control section 107 forms an update device in the invention.The main control section 107 updates or adds unique information in or tothe position-unique information database based on information providedby the position identification section 106 and in addition, updates oradds information in or to the current position, the position featureinformation stored in the storage section 110 and controls a move of themove section 109, origination of ultrasonic waves from the ultrasonicsensors 101, photographing of the camera 111, etc.

The main control section 107 updates the unique information registeredin the position-unique information database in response to change in theenvironment of a room. For example, to use the mobile robot 100 in aspace where a human being lives, the situation of the space changesmoment by moment and if the change is minute, there is a possibilitythat the accumulated error may become large affecting positionidentification. Thus, if the position of the mobile robot 100 isidentified as the position indicated by the lattice point in theposition-unique information database at the identifying time in theposition identification section 106, the main control section 107updates the signal unique information acquired from the uniqueinformation generation section 105 as the unique information inassociation with the lattice point indicating the current position.Accordingly, if the environment of the room changes, it is made possibleto identify the current position. The main control section 107 mayperform stepwise update processing rather than replacement of theinformation at a time, namely, may update the unique information usingunique information provided by combining the already registered uniqueinformation and newly acquired unique information at a proper ratio (forexample, combining the already registered unique information and newlyacquired unique information at a ratio of 9:1). As such stepwise updateprocessing is performed, it is made possible to reduce the effects ofthe disturbance elements of electric noise, reflected waves from a humanbeing, an animal, etc., happening to be present, etc.

If the feature amount extracted in the feature amount extraction section112 described later is output through the reference positiondetermination section 113, the main control section 107 stores thefeature amount in the position feature information in the storagesection 110 in association with position, attitude information of themobile robot 100 when photographed by the camera 111 described later.

The move section 109 forms a move device in the embodiment of theinvention. The move section is a mechanism required for the mobile robot100 to move under the control of the main control section 107. In theembodiment, a differential two-wheel mobile robot is adopted as themobile robot 100, but the move section 109 may be any move mode otherthan the wheel type used with the differential two-wheel mobile robot.For example, crawler type, walking type, etc., can be named.

The move distance detection section 108 acquires the move distance ofthe mobile robot 100 by the move section 109 and outputs the acquireddistance, etc., to the main control section 107. In the embodiment, themove distance is measured using any other sensor such as an encoderattached to the axle of the mobile robot 100. In the embodiment, themove distance is acquired by the move distance detection section 108,but the move distance detection section 108 is not necessarily requiredin the invention and the position identification section 106 describedlater may always identify the current position of the mobile robot 100.The move distance detected by the move distance detection section 108and identification of the current position of the mobile robot 100 bythe position identification section 106 are used in combination, wherebyit is made possible to identify the current position more accurately.

The camera 111 forms a detection device in the invention and photographsthe surrounding environment of the mobile robot 100 and outputs thephotographed image information to the feature amount extraction section112 under the control of the main control section 107. At the time offield search action or unique information collection action, the camera111 photographs the geometrical structure of the border between a walland a ceiling, a floor, a window frame, and a door frame under thecontrol of the main control section 107. The photographed image dataforms environment information in the invention. The sensor of the mobilerobot 100 other than the ultrasonic sensors 101 used for identifying theself-position is not limited to the camera 111 of an optical sensor andbased on the information detected by the sensor, the feature amountextraction section 112 may be able to extract the feature amountindicating the position.

The feature amount extraction section 112 forms extraction device in theinvention and extracts the shape of the pattern put on a wall, a floor,a ceiling, furniture, etc., as the feature amount from the image dataoutput from the camera 111 and outputs the extracted feature amount tothe reference position determination section 113.

The reference position determination section 113 forms a determinationdevice in the embodiment of the invention and makes a comparison betweenthe feature amount extracted by the feature amount extraction section112 and the feature amount included in the position feature informationstored in the storage section 110 and determines whether or not theposition photographed by the camera 111 is the reference position. Thereference position determination section 113 determines whether or notthe position photographed by the camera 111 is the reference positionnot only when the position-unique information database is prepared, butalso when the position information of the mobile robot 100 needs to bechecked or rest.

Next, a preparation procedure of the position-unique informationdatabase will be discussed. After the mobile robot 100 is firstinstalled in a room and a room drawing is acquired, the mobile robot 100collects unique information at the positions indicated by the latticepoints on the room drawing shown in FIG. 11. First, the main controlsection 107 described later provides lattice points indicating thecoordinates for collecting unique information on the acquired roomdrawing. For the spacing between the lattice points, a proper value isdetermined from the size of the mobile robot 100, the field width, theaccuracy of the used ultrasonic sensors 101, and the expectedself-position identifying range.

One of the positions indicated by the lattice points is the move startposition of the mobile robot 100 and the mobile robot 100 moves to theposition indicated by the next lattice point in sequence by the movesection 109 described later with the move start position as thereference. At this time, to eliminate a slip with the floor, the movesection 109 needs to move at lower speed than that at the usual time.When the mobile robot 100 arrives at the position indicated by thelattice point, the ultrasonic transmission section 102 for identifyingthe self-position transmits an ultrasonic wave, the ultrasonic receptionsection 103 receives the reflected wave, and the unique informationgeneration section 105 generates signal unique information. The maincontrol section 107 acquires the generated signal unique information andadds the acquired signal unique information to the position-uniqueinformation database as the unique information in association with thecollection point.

FIG. 13 shows a move path when the position-unique information databaseis generated. In the figure, with the move start origin of the mobilerobot 100 (g, 1) as the reference position, the camera 111 photographsthe surrounding environment from the reference position and the featureamount extraction section 112 extracts the feature amount from thephotographed image data under the control of the main control section107. At this time, the reference position determination section 113 doesnot process the feature amount and outputs the feature amount intact tothe main control section 107, which then stores the feature amount inthe storage section 110 as position feature information in associationwith the coordinates of the reference position and the attitude of themobile robot 100. The stored feature amount is adopted as the referencefeature amount. Then, the mobile robot 100 collects associated uniqueinformation at the positions indicated by the lattice points from theposition (g, 1) to a position (e, 1) in a path (1) and then returns tothe reference position and the camera 111 again photographs thesurrounding environment. The feature amount extraction section 112extracts the feature amount from the photographed image data. Next, thereference position determination section 113 determines whether or notthe feature amount matches the feature amount associated with thereference position in the position feature information first stored inthe storage section 110. If it is determined that the feature amountsmatch, the reference position is determined the current position of themobile robot 100; if it is not determined that the feature amountsmatch, the reference position is not determined the current position ofthe mobile robot 100. The determination result is output to the maincontrol section 107. Upon reception of the determination result to theeffect that the current position is not the reference position, the maincontrol section 107 determines that the current position shifts from thereference position, and moves the mobile robot 100 by the move section109 to correct the shift. Upon reception of the determination result tothe effect that the current position is the reference position, the maincontrol section 107 determines that the current position is thereference position, and does not correct the position. Then, the mobilerobot 100 moves from a position (g, 2) to a position (e, 2) in a path(2), acquires unique information at the position indicated by eachlattice point, again returns to the reference position from a path (3),determines whether or not the current position is the referenceposition, and correct shift. A similar procedure is also executed in apath (4) and the later, whereby it is made possible to accuratelyacquire the unique information to be registered in the position-uniqueinformation database.

When the unique information is collected to generate the position-uniqueinformation database, prefiltering of applying temperature compensation,a weight function, etc., may be performed in response to the situationin addition to filtering of the filtering section 104 and noise removalmade by filtering. Further, if the mobile robot 100 prepares a roomdrawing, the unique information for identifying the self-position may becollected after or at the same time as the search action to prepare theroom drawing.

Next, an example of usual processing after collection of the uniqueinformation of the mobile robot 100 according to the embodimentdescribed above will be discussed. FIG. 14 is a flowchart to show aprocedure example of the usual processing of the mobile robot 100according to the embodiment. The usual processing of the mobile robot100 is not limited to the following procedure.

The mobile robot 100 moves by the move section 109 (step S1301). Themobile robot 100 may move following the user or going round to detect ananomaly in the room and the move purpose is not limited. In theembodiment of the invention, the move is called a free move and isdistinguished from the move for generating the position-uniqueinformation database, etc.

The move distance detection section 108 of the mobile robot 100 acquiresthe move distance of the move section 109, etc., (step S1302).

The main control section 107 acquires the move distance from the movedistance detection section 108 and acquires the current position afterthe move from the move distance and the current position stored in thestorage section 110 indicating the position before the move (stepS1303). The main control section 107 determines whether or not thetiming is the timing for identifying the current position (step S1304).It is considered that the determination criterion as to whether or notthe timing is the timing for identifying the current position may be setas the reference based on which it can be determined that there is apossibility that the current position may shift due to a slip, etc.,because of move of a preset move distance or the expiration of a giventime. However, the invention is not limited to them; for example, thecurrent position may always be identified after the mobile robot 100moves.

If the main control section 107 does not determine that the timing isthe timing for identifying the current position (NO at step S1304), themain control section 107 updates the current position stored in thestorage section 110 to the current position acquired at step S1303 (stepS1310).

If the main control section 107 determines that the timing is the timingfor identifying the current position (YES at step S1304), the ultrasonictransmission section 102 transmits an ultrasonic wave under the controlof the main control section 107 (step S1305), and also outputs theidentification code of the transmitted ultrasonic wave to the differentrobot signal removal section 114.

The ultrasonic reception section 103 receives the reflected wave of thetransmitted ultrasonic wave (step S1306), and outputs the receivedreflected wave to the different robot signal removal section 114.

The different robot signal removal section 114 outputs only thereflected wave involved in the mobile robot 100 to the filtering section104 based on the identification code of the ultrasonic wave (stepS1307). Specifically, the different robot signal removal section 114determines whether or not the identification code of the ultrasonic waveinput from the ultrasonic reception section 103 at the originating timematches the identification code of the ultrasonic wave received from theultrasonic reception section 103. If they do not match, the differentrobot signal removal section 114 removes the signal of the ultrasonicwave as an ultrasonic wave of any other mobile robot 100 or noise; ifthey match, the different robot signal removal section 114 outputs thereflected wave to the filtering section 104 as the signal of theultrasonic wave involved in the mobile robot 100.

The filtering section 104 removes noise from the reflected wave outputfrom the different robot signal removal section 114 (step S1308). Theunique information generation section 105 acquires signal uniqueinformation based on the reflected wave with noise removed (step S1309).The position identification section 106 identifies the current positionfrom the acquired signal unique information and the association of theposition and unique information with each other, retained in theposition-unique information database in the storage section 110 (stepS1310). The detailed identification method of the positionidentification section 106 is described later. The main control section107 updates the current position stored in the storage section 110 tothe identified current position (step S1311).

Then, again the processing procedure is started at free move of themobile robot 100 by the move section 109 (step S1301).

In the embodiment, it is assumed that the mobile robot 100 stops whenthe current position of the mobile robot 100 is identified, but theinvention is not limited to the mode. If the move distance of the mobilerobot 100 is small relative to the fly time of an ultrasonic wave, thecurrent position of the mobile robot 100 can also be identified whilethe mobile robot 100 is moving.

Next, the identification processing of the current position performed bythe position identification section 106 at step S1310 in FIG. 14 will bediscussed. FIG. 15 is a flowchart to show a processing procedure ofidentifying the current position in the position identification section106 according to the embodiment.

First, the position identification section 106 determines that allsensors are comparison targets for identification (step S1401), acquiresthe signal unique information provided by totalizing the signal uniqueinformation of all sensors from the unique information generationsection 105 (step S1402), acquires the unique information provided bytotalizing the unique information of all sensors associated with theposition (b, 3) from the position-unique information database (stepS1403), and calculates the correlation value (step S1404). Thecorrelation value refers to the match degree between the signal uniqueinformation acquired from the unique information generation section 105and the unique information acquired from the position-unique informationdatabase.

A calculation expression (expression 1) for calculating the correlationvalue, used when the signal unique information and the uniqueinformation are each the signal strength of the reflected wave changingwith the time elapsed since the reference time at which ah ultrasonicwave was transmitted as in the embodiment is as follows:

$\begin{matrix}{{{{Sxy} = {\sum\limits_{i = 1}^{t}\left( {{{\delta\lbrack i\rbrack} - {\delta\;{{xy}\lbrack i\rbrack}}}} \right)}}{{\delta\lbrack i\rbrack}\left( {{i = 1},2,3,{\ldots\mspace{11mu} t}} \right)\text{:}\mspace{14mu}{unique}\mspace{14mu}{information}\mspace{14mu}{measured}\mspace{14mu}{at}\mspace{14mu}{free}\mspace{14mu}{moving}\mspace{14mu}{time}}{\delta\;{{xy}\lbrack i\rbrack}\left( {{i = 1},2,3,{\ldots\mspace{11mu} t}} \right)\text{:}\mspace{14mu}{unique}\mspace{14mu}{information}\mspace{20mu}{at}\mspace{14mu}{coordinates}\mspace{14mu}\left( {x,y} \right)\mspace{14mu}{rerorded}\mspace{14mu}{in}\mspace{14mu}{database}}}\mspace{11mu}} & \left\lbrack {{Expression}\mspace{20mu} 1} \right\rbrack\end{matrix}$

Difference sum Sxy between the signal unique information acquired fromthe unique information generation section 105 every given time intervalfrom the reference time and the unique information associated with theposition (b, 3) acquired from the position-unique information databaseis calculated. The reciprocal of Sxy is adopted as the correlation valueat the position (b, 3). It is determined that the higher the correlationvalue, the higher the correlation between the current position and theposition (b, 3). The correlation value calculation method is not limitedto the method and may be any method if the value changing depending onthe type of unique information and indicating the correlation betweenthe current position and the position retained in the position-uniqueinformation database can be calculated.

Referring again to FIG. 15, after the correlation value calculationterminates, the position identification section 106 determines whetherthe correlation value has been calculated for all positions retained inthe position-unique information database (step S1405). If the positionidentification section 106 determines that the correlation value is notcalculated for all positions (NO at step S1405), the positionidentification section 106 returns to step S1403 and again acquires theunique information provided by totalizing the unique information of allsensors associated with a different position for which correlation valuecalculation is not yet performed from the position-unique informationdatabase.

The correlation value is calculated for all positions retained in theposition-unique information database according to the proceduredescribed above. FIG. 16 is a conceptual drawing wherein a comparison ismade between the signal unique information acquired from the uniqueinformation generation section 105 and the unique information retainedin the position-unique information database and the correlation valuefor each position is calculated. In the figure, (A) indicates the signalunique information acquired from the unique information generationsection 105, the correlation value for each position is calculated usingthe signal unique information and the unique information for eachposition retained in the position-unique information database, thecorrelation value calculation result of all positions is shown below thearrow, and the higher the correlation at each position on the roomdrawing, the darker represented the color. In the embodiment, thecorrelation value is calculated for all positions, but the invention isnot limited to the mode. For example, if the mobile robot 100 recognizesthe current position by position identification, the correlation valuebetween the signal unique information and the unique information at theposition is calculated for determining the self-position and if thecorrelation value is not higher than a threshold value, the correlationvalue may be calculated for all positions.

Referring again to FIG. 15, if the position identification section 106determines that the correlation value has been calculated for allpositions (YES at step S1405), the position identification section 106complements the space between the lattice points indicating thepositions using a proper function from the correlation value for eachposition, thereby generating a mountain-like distribution of thecorrelation values concerning the whole field plane indicating the room(step S1406).

FIG. 17 shows the generated mountain-like distribution of thecorrelation values. The position indicating the crest of themountain-like distribution (A) on the field plane becomes the mostpossible position of the current position of the mobile robot 100.

Referring again to FIG. 15, whether or not the correlation value of thecrest of the mountain-like distribution of the correlation values ishigher than a predetermined threshold value is determined (step S1407).If the correlation value of the crest is determined higher than thethreshold value (YES at step S1407), the position indicating the crestof the mountain-like distribution on the field plane is identified asthe current position (step S1409). The threshold value refers to apredetermined correlation value used as the reference for identifyingthe current position. If the correlation value is higher than thethreshold value, it can be estimated that the position associated withthe correlation value is the current position. The actual thresholdvalue is determined based on the measurement result.

If the correlation value of the crest is determined lower than thethreshold value (NO at step S1407), it is determined that anyone or moresensors are comparison targets (step S1408) and the process returns tostep S1402 and the signal unique information provided by totalizing thesignal unique information of any determined sensors is acquired from theunique information generation section 105.

For example, if the sensors are the eight sensors shown in FIG. 9, the“anyone or more sensors” are the sensors assigned odd numbers. Thus, theposition identification section 106 calculates the correlation valuebased on the signal unique information and the unique information infour directions having the relation of phase difference 90 degrees. Inthis case, to calculate the correlation value at step S1404, theposition identification section 106 needs not only to calculate thecorrelation value from the signal unique information provided bytotalizing the signal unique information of the sensors assigned the oddnumbers acquired from the unique information generation section 105 andthe unique information provided by totalizing the unique information ofthe sensors of the odd numbers in the position-unique informationdatabase, but also to calculate the correlation value with the uniqueinformation provided by totalizing the unique information of the sensorsof even numbers in the position-unique information database. Amountain-like distribution of the former correlation values and that ofthe latter correlation values are generated and the higher crest isassumed to be the most possible position of the current position. If thecurrent position cannot be identified because the correlation value islower than the threshold value in comparison using the sensors assignedthe odd numbers, it is determined that the sensors assigned the evennumbers are comparison targets (step S1408) and the process returns tostep S1402 and the signal unique information provided by totalizing thesignal unique information of any determined sensors is acquired from theunique information generation section 105. As the comparison targets forcomparison with the unique information are thus narrowed to any one ormore sensors, ultrasonic measurement in any desired direction can beavoided for identifying the current position. Thus, if an exceptionalobstacle, such as a human being or an animal, exists in the vicinity ofthe mobile robot 100, it is made possible to avoid the direction of theobstacle for identifying the self-position.

In the embodiment, first the current position is identified with allsensors as the position identification processing, but the invention isnot limited to the mode. After the sensors to be used for identificationare narrowed from the beginning, the correlation value with the uniqueinformation may be calculated based on the signal unique informationprovided by totalizing the signal unique information of the sensors.Further, the value of the crest of the mountain-like distribution of thecorrelation values is compared with the threshold value and only if thevalue exceeds the threshold value, the position of the crest isidentified as the current position, but the position of the crest may beidentified intact as the current position without providing thethreshold value.

Further, the correlation value may be calculated based on the signalunique information provided by totalizing the signal unique informationof all sensors, whereby the operation processing is lightened and it ismade possible to identify the current position at high speed.

The identification method of the current position is not limited to theidentification of the current position based only on the correlationvalue calculation. The self-position may be identified together withdetection of the move distance with any other sensor, in the embodiment,the move distance detection section 108 for detecting the move distance.For example, if there are two or more crests of a generatedmountain-like distribution of the correlation values because of astructure problem of a room, the move distance is calculated by the movedistance detection section 108 and is used to identify the currentposition, whereby it is made possible to identify any mountain crest asthe current position of the mobile robot 100 and it is made possible toidentify the current position more accurately.

In the embodiment, if the current position of the mobile robot 100 isidentified, further it is also made possible for the positionidentification section 106 to identify the azimuth of the mobile robot100. FIG. 18 shows a processing procedure until determination of theazimuth of the mobile robot 100.

After identifying the current position of the mobile robot 100, theposition identification section 106 compares the signal uniqueinformation of each sensor acquired from the unique informationgeneration section 105 with the unique information of each sensorassociated with the position with the highest correlation value acquiredfrom the position-unique information database (step S1701). For example,the position identification section 106 compares the signal uniqueinformation of the first sensor in FIG. 9 acquired from the uniqueinformation generation section 105 with the unique information of eachsensor in the position-unique information database to find the sensorwith the highest correlation value.

The position identification section 106 acquires the relative anglebetween the first sensor and the sensor with the highest correlationvalue (step S1702) and identifies the absolute azimuth of the mobilerobot 100 from the relative angle and the initial direction previouslystored in the position-unique information database, namely, the initialdirection of the mobile robot 100 at the initial information settingtime for generating unique information (step S1703).

Accordingly, it is made possible for the mobile robot 100 to identifythe absolute azimuth without including an azimuth detection unit. In theembodiment, the first sensor is used as the comparison target, but thenumber of the comparison target sensor is not limited.

If any sensor is used as a comparison target in the positionidentification processing procedure, the current position may be unableto be identified because the highest correlation value does not exceedthe threshold value or for any other reason. Processing untilidentification of the current position of the mobile robot 100 will bediscussed. FIG. 19 is a flowchart to show a processing procedure untilidentification of the current position if the mobile robot fails toidentify the current position in the position identification processingprocedure shown in FIG. 14 according to the embodiment.

First, a message of identification failure of the current position isinput from the position identification section 106 to the main controlsection 107 (step S1801). For example, the possible case is as follows:Since a room door is closed abruptly, the acquired signal uniqueinformation becomes different from the unique information retained inthe position-unique information database and it is made impossible toobtain a reliable correlation value at any positions.

Next, the main control section 107 sets the position found from thecurrent position stored in the storage section 110 and the move distancedetected by the move distance detection section 108 as a tentativecurrent position (step S1802). The mobile robot 100 searches for thereference position existing in the vicinity of the current position fromthe position feature information stored in the storage section 110 (stepS1803). The mobile robot 100 moves to the found reference position bythe move section 109 (step S1804). After moving to the referenceposition, the mobile robot 100 takes an attitude similar to that at thegeneration time and photographs the surrounding environment by thecamera 111 (step S1805). The feature amount extraction section 112extracts the feature amount from the photographed image data (stepS1806). The reference position determination section 113 makes acomparison between the extracted feature amount and the referencefeature amount retained as the position feature information (stepS1807). If the extracted feature amount and the reference feature amountequal (YES at step S1807), it is determined that the tentatively setcurrent position is correct. The mobile robot 100 moves to the positionof the lattice point in the position-unique information database nearestto the current position tentatively set at step S1802 and under thecontrol of the main control section 107, collects the signal uniqueinformation at the position and adds the collected signal uniqueinformation to the position-unique information database as the uniqueinformation in association with the lattice point indicating theposition aside from the already held unique information (step S1809). Ifthe extracted feature amount and the reference feature amount do notequal (NO at step S1807), the main control section 107 determines thatthe current position is lost. The mobile robot 100 makes a random movein the move field by the move section 109 and then searches for thecurrent position until the correlation value of the current positionexceeds the threshold value according to the current positionidentification procedure described with reference to FIG. 15 (stepS1808).

Such a processing procedure is executed, whereby if identification ofthe current position ends in failure, it is made possible to acquireinformation of the current position.

Different pieces of unique information are retained in theposition-unique information database in association with the sameposition, whereby if ultrasonic wave reflection information at the samepoint largely changes as a door or a window is opened, for example,depending on the room structure, it is made possible to identify thecurrent position. The procedure for identifying the current positionbased on different pieces of unique information is as follows: Thecorrelation value is calculated for each of the different pieces ofunique information corresponding to the position at step S1404 shown inFIG. 15, and the highest correlation value of the calculated correlationvalues is adopted as the current correlation value and is used togenerate a mountain-like distribution function of the correlation valuesfor identifying the current position of the mobile robot 100.

In the embodiment, when the current position of the mobile robot 100 isidentified, if the current position is identified as the positionindicating a lattice point in the position-unique information database,the unique information in the position-unique information database isupdated in association with the current position in response to theenvironment change; if it is confirmed that the position is the currentposition based on the reference position information althoughidentification of the current position ends in failure in the processingprocedure described with reference to FIG. 15, unique information isnewly added to the position-unique information database in associationwith the coordinates of the lattice point indicating the position.However, the invention is not limited to the mode. For example, even ifit is confirmed that the position is the current position based on thereference position information although identification of the currentposition ends in failure, the unique information in the position-uniqueinformation database may be updated in association with the coordinatesof the lattice point indicating the current position.

The position identification procedure in the embodiment is to comparethe acquired signal unique information with the unique informationassociated with the position previously retained for identifying theposition. In an often used method of using the arrival time of theprimary reflected wave of an ultrasonic wave, etc., a secondary ortertiary reflected wave of an ultrasonic wave, etc., transmitted from adifferent sensor enters another sensor earlier than the primaryreflected wave in the direction in an environment wherein an obstacle isof a complicated shape or if an object absorbing or dispersing anultrasonic wave, etc., exists in the move field, the reflected wavecannot be received and therefore accurate position measurement of anobstacle cannot be conducted. In the position identification procedurein the embodiment however, disturbance noise is also handled as uniqueinformation at the position, so that it is made possible to accuratelyidentify the current position even in a complicated environment.

Since the mobile robot 100 does not require installation of a mark, anexternal auxiliary signal, it is made possible to accurately identifythe current position even in an environment wherein such a mark cannotbe installed. Further, it is not necessary to change the sensor to beused in response to the environment and it is made possible to identifythe current position only with an ultrasonic sensor.

In the embodiment, an ultrasonic wave acquires the signal uniqueinformation; the ultrasonic wave originating time is used as thereference time and the signal strength of the reflected wave changingwith the elapsed time since the reference time is used as the signalunique information and the unique information for identifying theposition, so that it is made possible to identify the current positionat high speed with light load imposed on a computer without performinglarge data processing.

In the embodiment, the mobile robot 100 is adopted as the positionidentification apparatus of the invention, but the invention is notlimited to the mobile robot. The invention is not limited either toidentification of the current position after the mobile robot 100 moves;the current position can also be identified after the user, etc.,changes the installation location, etc.

(Modifications)

The invention is not limited to the specific embodiment described aboveand the following various illustrated modifications can be made:

(Modification 1)

In the embodiment described above, the directional ultrasonic sensors101 transmit and receive an ultrasonic wave at every arbitrary angle,but the installation of the ultrasonic sensors 101 is not limited to themode. For example, as shown in FIG. 20, ultrasonic sensor 101 isinstalled so that an ultrasonic wave transmitted from a cone-typeresonator 11 of one ultrasonic sensor 101 is omni directionallyuniformly dispersed radially using a reflecting plate 21 and thereflected wave returned from the radiation direction can also bereceived at the one ultrasonic sensor 101 through the reflecting plate21, so that it is made possible to transmit or receive an ultrasonicwave from or at the ultrasonic sensor 101 in parallel with the robotmove plane 202 and in the radiation direction. The reflecting plate 21forms a reflection device in the embodiment of the invention. If signalunique information is acquired based on the received reflected wave andis retained in the position-unique information database in associationwith the position as unique information, it is made possible to identifythe current position at low cost and at high speed. Since only oneultrasonic sensor 101 is included, it is impossible to identify thedirection based on the relative angle between the sensor receiving thereflected wave and the sensor in the position-unique informationdatabase. If such a reflection structure is included, the robot 100needs to contain an azimuth detection section using the earth'smagnetism, for example.

(Modification 2)

In the embodiment described above, the unique information is only thesignal strength of the reflected wave changing with the elapsed timesince the reference time at which an ultrasonic wave was transmitted,but the type of unique information retained in the position-uniqueinformation database in association with the position is not limited toone type, and different types of unique information can be retained inassociation with the position. In the modification, a frequencydistribution provided by conducting frequency analysis on the receivedreflected wave using FFT, etc., is retained in the position-uniqueinformation database as unique information in association with theposition in addition to the signal strength of the reflected wavechanging with the elapsed time since the reference time at which anultrasonic wave was transmitted, associated with the position. When thecurrent position is identified, the correlation value is found based onthe received reflected wave and thus in addition to the signal strengthof the received reflected wave, frequency analysis is conducted on thereflected wave to find a frequency distribution as unique information,and the correlation values are found based on the unique informationretained in the position-unique information database. The two types ofcorrelation values for each position are added together, a mountain-likedistribution is generated according to the sum of the correlationvalues, and the crest is identified as the current position, so that itis made possible to identify the current position based on the twodifferent types of unique information and it is made possible to enhancethe identification accuracy.

(Modification 3)

In the embodiment described above, the mobile robot has the function ofinputting map information from CAD data, design drawings, etc. Forexample, the mobile robot 100 includes a unit having any or some ofsensors such as a displacement sensor such as an encoder, a distancesensor such as an ultrasonic senor, and an image sensor such as anoptical camera, it is made possible to generate a room drawing bysearching while sensing if the mobile robot is installed on an unknownfield plane. When the room drawing is generated, unique information maybe collected. Accordingly, it is made possible to collect uniqueinformation efficiently and the need for the user to input a roomdrawing to the mobile robot can be eliminated.

As described above, the current position identification apparatus andthe current position identification method according to the inventionare useful for identifying the current position and are suitedparticularly for a mobile robot intended for identifying the currentposition by transmitting and receiving a signal.

1. A self-position identification apparatus comprising: (a) a storagedevice storing position association unique information associatingposition coordinates and unique information indicating a unique featureamount associated with the position coordinates; (b) a transmissiondevice transmitting a detection signal assigned identificationinformation; (c) a reception device receiving a reflection signalcorresponding to the detection signal transmitted by said transmissiondevice; (d) a generation device generating signal unique informationbased on a unique position from the reflection signal received by saidreception device; and (e) an identification device comparing between thesignal unique information generated by said generation device and theunique information associated with the position coordinates included inthe position association unique information and indentifying a currentposition, wherein: (f) said identification device compares between thesignal unique information generated by said generation device and theunique information included in the position association uniqueinformation stored in said storage device; (g) the identification devicecalculates the correlation value indicating the correlation between theposition coordinates associated with the unique information and thecurrent position; (h) the identification identifies the current positionbased on the calculated correlation value: (i) said identificationdevice complements a correlation value at a position different from theposition coordinates from the calculated correlation value; (j) theidentification device calculates a distribution of the correlationvalues corresponding to the position coordinates; and (k) theidentification device identifies the crest of the distribution of thecorrelation values as the current position.
 2. The self-positionidentification apparatus according to claim 1, wherein saididentification device compares between the signal unique informationgenerated by said generation device and the unique informationassociated with the position coordinates included in the positionassociation unique information, and wherein the unique informationcontained in the signal is closest to the unique information associatedwith the position.
 3. The self-position identification apparatusaccording to claim 1, further comprising: a filtering device removingnoise from the reflection signal received by said reception device. 4.The self-position identification apparatus according to claim 3 whereinthe filtering device removes noise from the reflection signal based on areference time predetermined for an elapsed time from transmission ofthe detection signal by said transmission device to reception of thereflection signal by the reception device.
 5. The self-positionidentification apparatus according to claim 4 wherein the filteringdevice removes noise from the reflection signal based on a plurality ofreference times.
 6. The self-position identification apparatus accordingto claim 1,wherein said transmission device includes a plurality oftransmission sections annularly disposed each transmission sectiontransmitting the detection signal having directivity and wherein saidreception device includes a plurality of reception sections annuallydisposed each reception section receiving the reflection signalscorresponding to the detection signals transmitted from the transmissionsections.
 7. The self-position identification apparatus according toclaim 1, wherein said transmission device includes a transmissionsection rotating on an axis, wherein the transmission device transmitsthe detection signal having directivity at every arbitrary angle,wherein said reception device includes a reception section rotating onthe axis, and wherein the reception device receives the reflectionsignal corresponding to the detection signal transmitted from saidtransmission section.
 8. The self-position identification apparatusaccording to claim 1, further comprising: a reflection device radiallyreflecting the detection signal transmitted from a direction andreflecting the reflection signal in the direction, wherein the detectionsignal transmitted from said transmission device is transmitted radiallythrough the reflection device, and wherein said reception devicereceives the reflection signal through the reflection device.
 9. Theself-position identification apparatus according to claim 6, whereinsaid storage device stores the unique information in association foreach angle information indicating an angle between the receptiondirection receiving the reflection signal in the position coordinatesand a previously stored initial direction as the position associationunique information, wherein said generation device generates signalunique information associated with angle information calculated from thereception direction receiving the reflection signal by the receptionsection and a reference direction of the reception section, wherein saidself-position identification apparatus further includes a device,wherein the device compares between the signal unique informationgenerated by said generation device and the unique information includedin the position association unique information, and wherein the devicecalculates a relative angle between the initial direction and thereference direction on the basis of angle information associated withthe unique information closest to the generated signal uniqueinformation.
 10. The self-position identification apparatus according toclaim 1 wherein said storage device stores the position coordinates andthe signal unique information generated by said generation device,associated with the position coordinates in association as the positionassociation unique information.
 11. The self-position identificationapparatus according to claim 1, further comprising: a removal deviceremoving the reflection signal based on identification information ofthe reflection signal received by said reception device.
 12. Theself-position identification apparatus according to claim 11 wherein theidentification information assigned to the detection signal is a signalwith the transmission interval coded, and the identification informationof the reflection signal is a signal with the reception interval coded.13. The self-position identification apparatus according to claim 1wherein said storage device stores reference position coordinates andfeature information indicating the feature of the reference positioncoordinates in association with each other as reference position featureinformation, and wherein said self-position identification apparatusfurther includes: a detection device detecting environment informationat the current position; an extraction device extracting currentposition feature information indicating the feature of the currentposition from the environment information detected by the a detectiondevice; and a determination device comparing between the currentposition feature information extracted by the extraction device and thefeature information included in the reference position featureinformation and determining whether or not the current position is thereference position.
 14. The self-position identification apparatusaccording to claim 1, further comprising: an update device updating thecurrent position identified by said identification device and the signalunique information generated by said generation device in associationwith each other in the position association unique information stored insaid storage device.
 15. A self-position identification methodcomprising: (a) storing with a storage device position associationunique information provided by associating position coordinates andunique information indicating a unique feature amount associated withthe position coordinates; (b) transmitting a detection signal assignedidentification information; (c) receiving a reflection signalcorresponding to the transmitted detection signal; (d) generating with ageneration device signal unique information based on a unique positionfrom the received reflection signal; (e) comparing with anidentification device between the generated signal unique informationand the unique information associated with the position coordinatesincluded in the position association unique information; (f) identifyinga current position; (g) comparing the signal unique informationgenerated by said generation device and the unique information includedin the position association unique information stored in said storagedevice, and (h) calculating the correlation value indicating thecorrelation between the position coordinates associated with the uniqueinformation and the current position; and wherein: (i) saididentification device complements a correlation value at a positiondifferent from the position coordinates from the calculated correlationvalue; (j) the identification device calculates a distribution of thecorrelation values corresponding to the position coordinates, and (k)the identification device identifies the crest of the distribution ofthe correlation values as the current position.
 16. The self-positionidentification method according to claim 15 wherein, when the currentposition is identified, the position coordinates associated with theunique information closest to the signal unique information among thepieces of the unique information included in the position associationunique information is identified as the current position, while thesignal unique information generated at said generation step and theunique information associated with the position coordinates included inthe position association unique information are compared.
 17. Theself-position identification apparatus according to claim 6, whereineach transmission section simultaneously transmits the detection signalhaving directivity.